Monday, 7 March 2011

The apparent discovery of a new planet in our own solar system has been generating a lot of media buzz recently. Beginning with an article in the Independent, many media outlets have followed with bold claims about the announcement. CNN.com even ran it as their lead story.

However, whilst the existence of this object is plausible, it's not yet time for another planetary recount.

The hypothetical planet, dubbed "Tyche", was proposed by astrophysicists John Matese and Daniel Whitmire from the University of Louisiana at Lafayette. Their paper was published in the November 2010 edition of the scientific journal Icarus.

They believe the object to be either a very large gas giant or a brown dwarf star. They describe it as more of a companion to the Sun than a typical planet, orbiting far out in the (also hypothetical) Oort cloud.

Their hypothesis is based on observations of comet orbits. The duo point to a statistical bias in the origins of comets from the Oort cloud, claiming that comets do not appear randomly from the cloud but rather in a pattern that could be explained by the presence of a large planet.

Their claim is not new, in fact they first proposed this scenario back in 1999. Their latest paper builds on the original hypothesis with the assertion that statistical evidence is growing.

"What's new is that this pattern has persisted," said Matese. "It's possible that it's a statistical fluke, but that likelihood has lessened as more data has accumulated in the past 10 years."

Other astronomers are less convinced. Space.com spoke to planetary scientist Matthew Holman from the Harvard Smithsonian Institute of Astrophysics, who said: "Based on past papers that I've seen looking at where long-period comets came from in the sky, and finding signatures of large perturbers of the Oort cloud, I was not persuaded by the evidence."

Hal Levison, planetary scientist at the Southwest Research Institute in Boulder, Colorado, agreed: "What Matese claims is that he sees an excess of comets coming from a particular place, which he attributes to the gravitational effects of a large planet in the Oort cloud. I have nothing against the idea, but I think the signal that he claims he sees is very subtle, and I'm not sure it's statistically significant."

The next obvious step is to try and locate Tyche with a telescope. Unfortunately it would be too dim for a visible light telescope to see, but it would probably be detectable in infrared wavelengths. For this reason Matese and Whitmire are hoping for support from NASA's infrared space telescope WISE, which they believe will confirm Tyche's existence and location within two years.

According to Whitney Clavin of JPL, "It is likely but not a foregone conclusion that WISE could confirm whether or not Tyche exists. Since WISE surveyed the whole sky once, then covered the entire sky again in two of its infrared bands six months later, WISE would see a change in the apparent position of a large planet body in the Oort cloud over the six-month period."

Another possible method of detection, suggested by an audience member at a recent HAS public night, would be to look for a corresponding wobble in the Sun's position (known as the astrometric technique of planet detection). However Tyche's proposed orbital period is approximately 27 million years, ruling out this method for now. As an aside, Matese and Whitmire claim the 27 million year orbit could explain mass extinctions on Earth.

Whatever the eventual outcome, this story serves as a reminder that new scientific "discoveries" announced in mainstream media should always be taken with a grain of salt.